Interference mitigation in automotive radar systems by artificial doppler modulation

ABSTRACT

A method of operating an automotive radar system that includes a radar transmitter unit for transmitting radar waveforms towards a scene, a radar receiving unit for receiving radar waveforms that have been reflected by a target in the scene, and an evaluation and control unit for decoding range-Doppler information from the received waveforms. The method includes: transmitting a first sequence of radar waveforms (x Tx ) and a second sequence of radar waveforms ({tilde over (x)} Tx,k ) towards the scene that differs from the first transmitted sequence of radar waveforms (x Tx ) by predetermined phase shifts (φ k ) such that each radar waveform ({tilde over (x)} Tx,k ) of the second sequence has a different predetermined phase shift (φ k ). First range-Doppler information and second range-Doppler information are decoded. Deviations of the second range-Doppler information from the first range-Doppler information are compared to at least one predetermined deviation value. Based on the results of the comparing, a potential interference condition is identified.

TECHNICAL FIELD

The present invention generally relates to a method of operating anautomotive radar system for avoiding interference by other radarsystems, and to an automotive radar system operable pursuant to suchmethod.

BACKGROUND OF THE INVENTION

It is known in the art to employ radar technology in exterior automotiveapplications, such as driver assistance systems, for providing improvedsafety by facilitating an optimized reaction of a driver of a vehiclewith appropriate warnings such as vulnerable road user detectionsystems, lane change assist systems or blind spot monitoring systems, oreven by automatically taking over control of the vehicle, for instancein collision mitigation systems. The most common exterior automotiverated devices operate at radar carrier frequencies in a regime about 24GHz or about 77 GHz.

With the rapid spread of exterior automotive radar devices, mutualinterference of different road users has been recognized as a potentialproblem, which has been studied in detail in European Union programMOSARIM (MOre Safety for All by Radar Interference Mitigation) between2010 and 2012. Possible effects of mutual interference besides a generalincrease of noise level are a masking of targets and an appearance ofghost targets. The MOSARIM program identified and evaluated interferencemitigation techniques in the polarization domain, the time domain, thefrequency domain, the coding domain and the space domain.

An analysis of mutual interference mechanisms of automotive radarsystems is provided, for instance, in the article by G. Brooker, “MutualInterference of Millimeter-Wave Radar Systems,” IEEE Trans. Electromagn.Compat., vol. 49, no. 1, pp. 170-181, February 2007. Genericinterference scenarios and a current status at that time is provided inthe article by M. Goppelt et al., “Automotive radar—investigation ofmutual interference mechanisms”, Adv. Radio Sci., vol. 8, pp. 55-60,2010. Both these documents shall hereby be incorporated by reference intheir entirety with effect for those jurisdictions permittingincorporation by reference.

Further, interference mitigation techniques have also been proposed inpatent literature. For example, patent application publication DE 195 46653 A1 describes a method for reducing mutual interference of pulseDoppler radar devices. Individual transmitted bursts are composed oftransmission pulses which have different phase shifts according to apredetermined code from transmission pulse to transmission pulse. In areceive path, the phase shifts of the received echoes are decodedaccording to the predetermined code, i.e. are compensated or are takeninto account or evaluated during an evaluation according to thepredetermined code.

European patent application EP 1 821 118 A1 proposes a search/detectionapparatus comprising a generation device for modulating a carrier signalby a modulation signal and generating a probe signal for detectinglocation of a target; a transmitting sensor for radiating the probesignal; a receiving sensor for receiving the probe signal reflected bythe target as an echo signal; an extraction device for extractingdistance information about the target from the echo signal; aninterference detection device for detecting existence of an interferencesignal other than the echo signal from a signal received by thereceiving sensor and outputting a detection signal; and a control devicefor modifying a parameter of the modulation signal when receiving thedetection signal from the interference detection device. The controldevice can modify at least one of an initial time, a phase, and a cycleof the modulation signal as the parameter of the modulation signal.

SUMMARY

It is therefore an object of the invention to provide an automotiveradar system with an improved mitigation of potential interference, forexample by other automotive radar systems.

In one aspect of the present invention, the object may be achieved by amethod of operating an automotive radar system for avoiding interferenceby other radar systems. The automotive radar system includes a radartransmitter unit, a radar receiving unit and an evaluation and controlunit. The radar transmitter unit is configured to transmit radarwaveforms having a radar carrier frequency towards a scene. The radarreceiving unit is configured for receiving radar waveforms that havebeen transmitted by the radar transmitter unit and have been reflectedby a target in the scene. The evaluation and control unit is configuredfor decoding range-Doppler information from the radar waveforms receivedby the radar receiving unit.

The term “automotive radar system”, as used in this application, shallparticularly be understood to encompass radar systems for vehicles suchas but not limited to passenger cars, trucks and buses. The phrases“configured for” and “configured to”, as used in this application, shallin particular be understood as being specifically programmed, laid out,furnished or arranged.

As is well known in the art, automotive radar systems can be configuredfor transmitting radar waves in a modulated continuous mode, forinstance in frequency-modulated continuous wave (FMCW) radar systems, inwhich a time delay between a transmitted radar wave and a received radarwave, which is a transmitted radar wave reflected by a target, isdetermined by both a range between target and radar system and avelocity of the target with respect to the radar system (Dopplereffect). A separation between the effects of range and velocity can becarried out by applying well-known techniques, for instance triangularradar wave modulation or alternate transmission of modulated andunmodulated radar waves. The phrase “range-Doppler information”, as usedin this application, shall particularly be understood as the informationincluded in the received radar waves before a separation of the effectsof range and velocity is performed.

According to this first aspect of the invention, the method comprisessteps of:

-   -   transmitting a first sequence of radar waveforms towards a        scene,    -   receiving first radar waveforms that have been reflected by a        target hit by the transmitted first sequence of radar waveforms,    -   decoding first range-Doppler information from the received first        radar waveforms,    -   transmitting at least a second sequence of radar waveforms        towards the scene that differs from the first transmitted        sequence of radar waveforms by predetermined phase shifts such        that each radar waveform of the second sequence has a different        predetermined phase shift,    -   receiving second radar waveforms that have been reflected by the        target hit by the transmitted second sequence of radar        waveforms,    -   decoding second range-Doppler information from the received        second radar waveforms,    -   comparing deviations of the first range-Doppler information from        the second range-Doppler information to at least one        predetermined deviation value, and    -   based on the results of the comparing, identifying a potential        interference condition.

Advantageously, by applying decoding techniques known per se to thereceived second radar waveforms, there results a predefined signal shiftwith respect to the received first radar waveforms. The predefinedsignal shift can be used to ‘mark’ signals obtained from a sequence ofradar waveforms transmitted by the automotive radar system itself, as itdoes not occur in radar waves transmitted by and unintentionallyreceived from other automotive radar systems. By marking the signalsobtained from the radar waveforms transmitted by the automotive radarsystem itself, potential interference from other automotive radarsystems can be identified. The chances of a potentially interferingautomotive radar system performing an identical predefined signal shiftcan virtually be excluded.

The potential interference condition can, for instance, be accounted forby simply detecting that a function of the automotive radar system isaffected by interference, by identifying ghost targets and/or by findingtargets that are hidden in interference patterns. For example, anyportion of a decoded signal that does not show the predefined signalshift and that exceeds a predetermined threshold value for a signalamplitude may trigger a detection of the automotive radar system beingaffected by interference. As another example, a portion of the decodedsignal that does not show the predefined signal shift and that indicatesa target in a specific range can be identified as a ghost target.

Those skilled in the art will readily acknowledge that the method inaccordance with the invention can also beneficially be applied toautomotive radar systems in which the range-Doppler information iscombined with additional spatial decoding, for example an angulardecoding.

It is further noted herewith that the terms “first”, “second”, etc. areused in this application for distinction purposes only, and are notmeant to indicate or anticipate a sequence or a priority in any way.

The radar transmitter unit can have one transmit antenna or more thanone transmit antennas for transmitting radar waveforms. The radarreceiving unit can have one receiving antenna or more than one receivingantennas for receiving radar waveforms that have been transmitted by thetransmit antenna(s) and have been reflected by a target in the scene.

Preferably, the transmit antennas of the radar transmitter unit and thereceiving antennas of the radar receiving unit are arrangeable in afront region of a vehicle.

In preferred embodiments of the method, the predetermined phase shiftsare based on a Doppler frequency derived from a predetermined velocityrelative to a target, and the radar carrier frequency. In this way, asubstantial and sufficiently large predefined signal shift can beaccomplished after decoding the received radar waveforms.

The chances of a potentially interfering automotive radar systemperforming an identical predefined signal shift can even be lowered ifthe predetermined velocity is randomly selected from a predeterminedrange of velocities.

In preferred embodiments of the method, the steps of transmitting asequence of radar waveforms include transmitting a plurality ofconsecutive radar waveforms of identical duration. In this way, thesteps of decoding can be carried out with a reduced effort.

Preferably, the step of decoding the first range-Doppler information andthe second range-Doppler information comprises sorting the respectiverange-Doppler information into a plurality of range gates and aplurality of Doppler bins, and the step of comparing deviationscomprises comparing a mutual shift between the range-Doppler informationalong the respective plurality of Doppler bins.

The decoding of the range-Doppler information can be carried out by thetechniques known in the art, for instance the twofold FFT in fast timeand slow time, respectively, that is commonly used in FMCW processing.By applying the proposed phase shift, the second range-Dopplerinformation will show a predetermined shift along the Doppler bins. Inthis way, the step of comparing deviations can readily be executed.

In preferred embodiments of the method, the step of decoding includesdechirping the received radar waveforms and carrying out either a fastFourier transform (FFT) or a correlation analysis at the dechirped radarwaveforms. This step of decoding can be beneficially applied inparticular for automotive radar systems designed as an FMCW radar system(FFT) or for automotive radar systems designed as an PMCW radar system(correlation analysis). Dechirping techniques are well-known in the artand therefore need not be discussed in more detail herein.

Preferably, the step of transmitting sequences of radar waveformstowards the scene comprises transmitting frequency-modulated orphase-modulated continuous radar waves towards the scene. In this way,the well-known advantages of frequency-modulated continuous wave (FMCW)radar systems or phase-modulated continuous wave (PMCW) radar systemscan readily be utilized. The assets and drawbacks of FMCW and PMCW radarsystems are, for instance, discussed in Levanon, N., and B. Getz:“Comparison between linear FM and phase-coded CW radars”, IEEProceedings-Radar, Sonar and Navigation 141.4 (1994), 230-240.

In another aspect of the invention, an automotive radar system isprovided that comprises a radar transmitter unit, a radar receiving unitand an evaluation and control unit. The radar transmitter unit isconfigured to transmit at least a sequence of radar waveforms towards ascene according to a first predetermined pattern. The radar waveformshave a radar carrier frequency. The radar receiving unit is configuredfor receiving radar waveforms that have been transmitted by the radartransmitter unit and have been reflected by a target in the scene. Theevaluation and control unit is configured for decoding range-Dopplerinformation from the radar waveforms received by the radar receivingunit.

The radar transmitter unit is further configured to transmit, atpredetermined points in time and/or in predetermined time intervals, asequence of radar waveforms according to a second predetermined patternthat differs from the first predetermined pattern by predetermined phaseshifts such that each radar waveform of the second sequence has adifferent predetermined phase shift.

The evaluation and control unit is configured to:

-   -   decode first range-Doppler information from radar waveforms        received after reflection of the sequence of radar waveforms        according to the first predetermined pattern at the target,    -   decode second range-Doppler information from radar waveforms        received after reflection of the sequence of radar waveforms        according to the second predetermined pattern at the target,    -   compare deviations of the first range-Doppler information from        the second range-Doppler information to at least one        predetermined deviation value, and to    -   identify, based on the result of the comparison, a potential        interference condition.

The benefits described in context with the method proposed herein applyto the automotive radar system to the full extent. The potentialinterference condition can be accounted for, for instance by simplydetecting that a function of the automotive radar system is affected byinterference, by identifying ghost targets and/or by finding targetsthat are hidden in interference patterns.

In preferred embodiments, the automotive radar system further comprisespluralities of range gates and pluralities of Doppler bins for sortingthe decoded first range-Doppler information and the decoded secondrange-Doppler information. Deviations of the first range-Dopplerinformation from the second range-Doppler information are indicated bymutual shifting of activated positions along the pluralities of Dopplerbins. In this way, the deviations can be identified in a particularlyeasy manner.

Preferably, the radar transmitter unit and the radar receiving unit forman integral part of a transceiver unit, wherein the radar transmitterunit and the radar receiving unit share a common circuitry and/or sharea common housing. Such an embodiment can provide a compact design and isespecially beneficial for building a monostatic automotive radar system.

Preferably, the evaluation and control unit comprises a processor unitand a digital data memory unit to which the processor unit has dataaccess. In this way, the steps of decoding and the steps of comparingdeviations and identifying a potential interference condition can beperformed within the automotive radar system in proximity to the radarreceiving unit to ensure a fast and undisturbed signal processing andevaluation.

In yet another aspect of the invention, a software module forcontrolling an automatic execution of steps of an embodiment of themethod disclosed herein is provided.

The method steps to be conducted are converted into a program code ofthe software module, wherein the program code is implementable in anon-transitory computer-readable medium such as a digital memory unit ofthe automotive radar system, and is executable by a processor unit ofthe automotive radar system. Preferably, the digital memory unit and/orprocessor unit may be a digital memory unit and/or a processing unit ofthe evaluation and control unit of the automotive radar system. Theprocessor unit may, alternatively or supplementary, be another processorunit that is especially assigned to execute at least some of the methodsteps.

The software module can enable a robust and reliable execution of themethod and can allow for a fast modification of method steps.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

It shall be pointed out that the features and measures detailedindividually in the preceding description can be combined with oneanother in any technically meaningful manner and show furtherembodiments of the invention. The description characterizes andspecifies the invention in particular in connection with the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the present invention will be apparentfrom the following detailed description of not limiting embodiments withreference to the attached drawing, wherein:

FIG. 1 schematically illustrates a configuration of an automotive radarsystem in accordance with the invention and targets in a scene, and

FIG. 2 is a flowchart of an embodiment of a method in accordance withthe invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a configuration of an automotive radarsystem 10 in accordance with an embodiment of the invention and targets26, 28 of a scene. The automotive radar system 10 is designed as afrequency-modulated continuous wave (FMCW) radar system and isinstallable in a vehicle such as a passenger car (not shown).

The automotive radar system 10 comprises a radar transmitter unit 12, aradar receiving unit 16 and an evaluation and control unit 20 that isconnected by data links to both the radar transmitter unit 12 and theradar receiving unit 16.

The radar transmitter unit 12 includes a radar transmit antenna 14 thatis directed towards the scene. The radar receiving unit 16 includes aradar receiving antenna 18 that is also directed towards the scene. Theradar transmit antenna 14 and the radar receiving antenna 18 areco-located in a monostatic arrangement, which is indicated in FIG. 1 byuse of a combined symbol. In this specific embodiment, the radartransmitter unit 12 and the radar receiving unit 16 form an integralpart of a transceiver unit. In other embodiments, the radar transmitterunit 12 and the radar receiving unit 16 may be designed as separateunits. The evaluation and control unit 20 comprises a processor unit 22and a digital data memory unit 24 to which the processor unit 22 hasdata access.

Controlled by the evaluation and control unit 20, the radar transmitterunit 12 is configured to transmit a sequence of radar waveforms x_(Tx)to the scene. The sequence of radar waveforms x_(Tx) is formed accordingto a first predetermined pattern, which is given by consecutivelytransmitted radar waveforms x_(Tx) of a predefined duration τ. Theindividual transmitted radar waveforms x_(Tx) have a radar carrierfrequency of about 77.0 GHz that is triangle wave frequency-modulated.

The radar receiving unit 16 is configured for receiving radar waveformsthat have been transmitted by the radar transmitter unit 12 and havebeen reflected by at least one of the targets 26, 28 in the scene.Signals generated by the radar receiving unit 16 are transferred to theevaluation and control unit 20 via the data link. The evaluation andcontrol unit 20 is configured for decoding range-Doppler informationfrom radar waveforms x_(Rx) received by the radar receiving unit 16 andcontinually processes received radar waveform excerpts x_(Rx) ofduration τ. The radar receiving unit 16 comprises pluralities of rangegates and pluralities of Doppler bins (not shown) for sorting thedecoded range-Doppler information.

The received radar waveform excerpts x_(Rx) are transformed in order todecode spatial information of the reflecting target 26, 28. This canformally be expressed by a mapping T(x_(Rx))=x_(α). In this specificembodiment, the transform T is given by a subsequent application of adechirp algorithm and a fast Fourier transform (FFT). In an alternativeembodiment, in which the automotive radar system may be designed as aphase-modulated continuous wave (PMCW) radar system, the transform maybe given by a subsequent application of a dechirp algorithm and acorrelation analysis.

In order to decode the Doppler frequency, the spatial decoding isrepeated for a plurality of N times, wherein N is a power of 2 selectedbetween 128 and 1024. That is, a sequence of transformed signalsT(x _(Rx,1))=x _(a,1) ;T(x _(Rx,2))=x _(a,2) ; . . . ;T(x _(Rx,N))=x_(a,N)is recorded for Doppler decoding.

Controlled by the evaluation and control unit 20, the radar transmitterunit 12 is configured to transmit, at predetermined points in time thatare timely spaced by a multiple of N·τ, a sequence of radar waveforms{tilde over (x)}_(Tx,k) according to a second predetermined pattern thatdiffers from the first predetermined pattern by predetermined phaseshifts φ_(k) such that each radar waveform {tilde over (x)}_(Tx,k) ofthe second sequence has a different predetermined phase shift φ_(k). Thesequence of radar waveforms {tilde over (x)}_(Tx,k) according to thesecond predetermined pattern is transmitted in lieu of the sequence ofradar waveforms x_(Tx) according to the first predetermined pattern.

The sequence of radar waveforms {tilde over (x)}_(Tx,k) according to thesecond predetermined pattern can be expressed ase ^(2πi·˜) ^(k) ·x _(Tx) for k=1,2, . . . ,N

In one approach, the predetermined phase shifts φ_(k) are based on aDoppler frequency f_(v) derived from a predetermined relative velocity vthat is randomly selected from a predetermined range of velocities,which in this specific embodiment is a range between 0.5 m/s and 10.0m/s for parking purposes, and is randomly selected as a velocity v of1.0 m/s, between the automotive radar system 10 and the target 26, 28,and the radar carrier frequency.

For a fixed relative velocity v between the automotive radar system 10and the target 26, 28, hence a fixed Doppler shift, the above transformundergoes a phase shift corresponding to the Doppler frequency f_(v)x _(a,k) ≈e ^(2πi·f) ^(v) ^(·k·τ) ·x _(a,1) for k=1,2, . . . ,N

The various Doppler shifts present in the radar-illuminated scenesuperimpose in the range gates and Doppler bins. Hence, the spatialinformation can be divided in separated Doppler bins by means of the FFTof length N in the single range gates.

In other words, transmission of the sequence of radar waveforms {tildeover (x)}_(Tx,k) according to the second predetermined pattern resultsin a predefined shift of the spatial information in the Doppler binswith respect to the transmission of the sequence of radar waveformsx_(Tx) according to the first predetermined pattern.

In the following, an embodiment of a method of operating the automotiveradar system 10 pursuant to FIG. 1 for avoiding interference by otherradar systems will be described. A flowchart of the method is providedin FIG. 2. In preparation of operating the automotive radar system 10,it shall be understood that all involved units and devices are in anoperational state and configured as illustrated in FIG. 1.

In order to be able to carry out the method automatically and in acontrolled way, the evaluation and control unit 10 comprises a softwaremodule 30 (FIG. 1). The method steps to be conducted are converted intoa program code of the software module 30. The program code isimplemented in the digital data memory unit 24 of the evaluation andcontrol unit 20 and is executable by the processor unit 22 of theevaluation and control unit 20.

All predetermined/predefined values, thresholds and tolerance marginsmentioned herein such as phase shifts, range of relative velocity,deviation value, radar waveform duration etc. reside in the digital datamemory unit 24 of the evaluation and control unit 20 and can readily beretrieved by the processor unit 22 of the evaluation and control unit20.

Referring now to FIG. 2, in a first step 32 of the method a firstsequence of N radar waveforms x_(Tx,1), x_(Tx,2), . . . , x_(Tx,N)according to the first predetermined pattern is transmitted over timeN·τ towards the scene.

In a next step 34 of the method, first radar waveform excerpts x_(Rx,1),x_(Rx,2), . . . , x_(Rx,N), each one of duration τ, are received thathave been reflected by the target 26, 28 hit by the transmitted firstsequence of radar waveforms x_(Tx). In another step 36, a firstrange-Doppler information is decoded as described before from thereceived first radar waveform excerpts x_(Rx,1), x_(Rx,2), . . . ,x_(Rx,N). As an interim result of the step 36 of decoding, transformedsignals T(x_(Rx,1))=x_(a,1); T(x_(Rx,2))=x_(a,2); . . . ;T(x_(Rx,N))=x_(a,N) are generated, which represent N times the rangeinformation of the reflecting target 26, 28. The first range-Dopplerinformation is derived by applying the FFT of length N over the singlerange gates. Then, in another step 38 of the method, a second sequenceof radar waveforms {tilde over (x)}_(Tx,k):=e^(2πi·f) ^(v)^(·τ)·x_(Tx,1); e^(2πi·f) ^(v) ^(·2τ)·x_(Tx,2); . . . ; e^(2πi·f) ^(v)^(·Nτ)·x_(Tx,1) is transmitted to the scene according to the secondpredetermined pattern, differing from the first predetermined pattern bythe predetermined phase shifts 2πi·f_(v)·kτ, which are based on theDoppler frequency f_(v) derived from the randomly selected predeterminedrelative velocity v of 1.0 m/s.

In a next step 40, second radar waveform excerpts {tilde over(x)}_(Rx,1), {tilde over (x)}_(Rx,2), . . . , {tilde over (x)}_(Rx,N) ofduration τ are received that have been reflected by the target 26, 28hit by the transmitted second sequence of radar waveforms {tilde over(x)}_(Tx,k). In another step 42, a second range-Doppler information isdecoded as described before from the received second radar waveformexcerpts {tilde over (x)}_(Rx,1), {tilde over (x)}_(Rx,2), . . . ,{tilde over (x)}_(Rx,N). As an interim result of the step 42 ofdecoding, transformed signals T({tilde over (x)}_(Rx,1))={tilde over(x)}_(a,1); T({tilde over (x)}_(Rx,2))={tilde over (x)}_(a,2); . . . ;T({tilde over (x)}_(Rx,N))={tilde over (x)}_(a,N) are generated, whichrepresent N times the range information of the hit target 26, 28. Thesecond range-Doppler information is derived by applying the FFT oflength N over the single range gates.

With respect to the first range-Doppler information, the secondrange-Doppler information is shifted along the Doppler bins in Dopplerdimension by the velocity v, which is a predetermined value.

A deviation of the second range-Doppler information from the firstrange-Doppler information is given by the shift along the Doppler binsby the predetermined velocity v. This deviation is compared to apredetermined deviation value for a shift along the Doppler bins in anext step 44 of the method.

In another step 46 of the method, based on the results of the step ofcomparing 44, a potential interference condition is identified in casethat the result of the comparison is negative, and ghost targets areidentified. In case that the deviation is equal to the predetermineddeviation value within predefined margins of tolerance, targets areidentified as being properly detected and regular operation of theautomotive radar system 10 can be confirmed, for instance by sending anappropriate information to an electronic control unit of the vehicle.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Other variations to be disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. In the claims, the word “comprising” does not excludeother elements or steps, and the indefinite article “a” or “an” does notexclude a plurality, which is meant to express a quantity of at leasttwo. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage. Any reference signs in the claimsshould not be construed as limiting scope.

The invention claimed is:
 1. A method of operating an automotive radarsystem for avoiding interference by other radar systems, the automotiveradar system including: a radar transmitter that is configured totransmit radar waveforms (x_(Tx), {tilde over (x)}_(Tx)) having a radarcarrier frequency towards a scene, a radar receiver that is configuredfor receiving radar waveforms (x_(Rx), {tilde over (x)}_(Rx)) that havebeen transmitted by the radar transmitter and have been reflected by atarget in the scene, and an evaluation and control unit that isconfigured for decoding range-Doppler information from the radarwaveforms (x_(Rx), {tilde over (x)}_(Rx)) received by the radarreceiver, the method comprising steps of: transmitting a first sequenceof radar waveforms (x_(Tx)) towards a scene, receiving first radarwaveforms (x_(Rx)) that have been reflected by a target hit by thetransmitted first sequence of radar waveforms (x_(Tx)), decoding firstrange-Doppler information from the received first radar waveforms(x_(Rx)), transmitting at least a second sequence of radar waveforms({tilde over (x)}_(Tx,k)) towards the scene that differs from the firsttransmitted sequence of radar waveforms (x_(Tx)) by predetermined phaseshifts (φ_(k)) such that each radar waveform ({tilde over (x)}_(Tx,k))of the second sequence has a different predetermined phase shift(φ_(k)), receiving second radar waveforms ({tilde over (x)}_(Rx,k)) thathave been reflected by the target hit by the transmitted second sequenceof radar waveforms ({tilde over (x)}_(Tx,k)), decoding secondrange-Doppler information from the received second radar waveforms({tilde over (x)}_(Rx,k)), comparing deviations of the secondrange-Doppler information from the first range-Doppler information to atleast one predetermined deviation value, and based on the results of thecomparing, identifying a potential interference condition.
 2. The methodas claimed in claim 1, wherein the predetermined phase shifts (φ_(k))are based on a Doppler frequency (f_(v)) derived from a predeterminedvelocity (v) relative to a target and the radar carrier frequency. 3.The method as claimed in claim 2, wherein the predetermined velocity (v)is randomly selected from a predetermined range of velocities.
 4. Themethod as claimed in claim 1, wherein the steps of transmitting asequence of radar waveforms include transmitting a plurality ofconsecutive radar waveforms (x_(Tx), {tilde over (x)}_(Tx,k)) ofidentical duration (τ).
 5. The method as claimed in claim 1, wherein thesteps of decoding the first range-Doppler information and the secondrange-Doppler information comprises sorting the respective range-Dopplerinformation into a plurality of range gates and a plurality of Dopplerbins, and the step of comparing deviations comprises comparing a mutualshift between the range-Doppler information along the respectiveplurality of Doppler bins.
 6. The method as claimed in claim 1, whereinthe steps of decoding include dechirping the received radar waveforms(x_(Rx), {tilde over (x)}_(Rx,k)) and carrying out either a fast Fouriertransform or a correlation analysis at the dechirped radar waveforms. 7.The method as claimed in claim 1, wherein the steps of transmittingsequences of radar waveforms (x_(Tx), {tilde over (x)}_(Tx,k)) towardsthe scene comprises transmitting frequency-modulated or phase-modulatedcontinuous radar waves towards the scene.
 8. An automotive radar system,comprising: a radar transmitter that is configured to transmit at leasta sequence of radar waveforms (x_(Tx)) towards a scene according to afirst predetermined pattern, the radar waveforms having a radar carrierfrequency, a radar receiver that is configured for receiving radarwaveforms (x_(Rx)) that have been transmitted by the radar transmitterand have been reflected by a target in the scene, an evaluation andcontrol unit that is configured for decoding range-Doppler informationfrom the radar waveforms (x_(Rx)) received by the radar receiver,wherein: the radar transmitter is further configured to transmit, atpredetermined points in time and/or in predetermined time intervals, asequence of radar waveforms ({tilde over (x)}_(Tx)) according to asecond predetermined pattern that differs from the first predeterminedpattern by predetermined phase shifts (φ_(k)) such that each radarwaveform ({tilde over (x)}_(Tx,k)) of the second sequence has adifferent predetermined phase shift (φ_(k)), and wherein: the evaluationand control unit is configured to: decode first range-Dopplerinformation from radar waveforms (x_(Rx)) received after reflection ofthe sequence of radar waveforms (x_(Tx)) according to the firstpredetermined pattern at the target, decode second range-Dopplerinformation from radar waveforms ({tilde over (x)}_(Rx,k)) receivedafter reflection of the sequence of radar waveforms ({tilde over(x)}_(Tx,k)) according to the second predetermined pattern at thetarget, compare deviations of the first range-Doppler information fromthe second range-Doppler information to at least one predetermineddeviation value, and identify, based on the result of the comparison, apotential interference condition.
 9. The automotive radar system asclaimed in claim 8, further comprising pluralities of range gates andpluralities of Doppler bins for sorting the decoded first range-Dopplerinformation and the decoded second range-Doppler information, whereindeviations of the first range-Doppler information from the secondrange-Doppler information are indicated by mutual shifting of activatedpositions along the pluralities of Doppler bins.
 10. The automotiveradar system as claimed in claim 8, wherein the radar transmitter andthe radar receiver form an integral part of a transceiver.
 11. Theautomotive radar system as claimed in claim 8, wherein the evaluationand control unit comprises a processor and a digital data memory towhich the processor has data access.
 12. A non-transitorycomputer-readable medium for controlling automatic execution of themethod as claimed in claim 1, wherein each of the transmitting,receiving, decoding, and comparing steps to be conducted are stored onthe computer-readable medium as a program code, wherein thecomputer-readable medium comprises a part of the automotive radar systemor a separate controller and is executable by a processor of theautomotive radar system or the separate controller.